For two thousand years, until the European Renaissance (1400–1600), the works of Plato and Aristotle went largely unchallenged. Since then human knowledge has advanced spectacularly, highlighting the flaws in their theories. Nevertheless, the two philosophers laid the foundations of modern thought in their attempt to understand themselves and the world.For Plato (427?–347BCE), knowledge was gained through deduction. In his Theory of the Forms (the material world as an imperfect copy of the unchanging world of ideas), Plato proposed that truth was acquired through knowledge of the Forms by way of reason — rather than through the senses. A chair, for instance, was only a chair because it ‘participated’ in the Form ‘chair’. One must, therefore, strive to understand the idea ‘chairness’, rather than examining individual examples of chairs.Plato’s pupil Aristotle (384–322BCE), the son of a physician, learned about nature by studying plants and animals as a boy. He departed from Plato’s teachings to emphasize the importance of observation in creating knowledge. His approach was based on inductive reasoning, which meant that one had to look into the world, at the object itself, in order to gain knowledge. This proto-scientific approach enabled him to write some of the first works on physics, zoology and biology.This disagreement between Plato and Aristotle is exemplified in Raphael’s The School of Athens (1509–11). In the painting, Plato is depicted pointing towards the sky, representing his world of ideas, whilst Aristotle gestures towards the earth, signifying the importance of exploring the material world.